How many of us at middle age yearn for the opportunity to reencounter a long-lost love? We show up at school reunions, searching for the ghost of romance past. Or perhaps we settle for a mutual "friending" on Facebook and a tepid e-mail or two.

The protagonists of Mary Gordon's intermittently affecting new novel, "The Love of My Youth," are more fortunate: They play out their second-chance fantasy against the backdrop of Rome's baroque splendor — a setting that conjures such classic film romances as "Roman Holiday" and "Three Coins in the Fountain."

Despite the well-worn magic of the city, the odds seem arrayed against Gordon's ex-lovers, Miranda and Adam. Both are pushing 60 and married fairly happily to other people. They have not spoken for almost four decades, since a bitter parting in 1971.

Now Miranda is in Rome for an environmental epidemiology conference and a solo vacation. Adam, a pianist-turned-music teacher, is living there while his daughter takes violin lessons. A mutual friend, Valerie, facilitates their meeting.

The setup of the novel is a bit clumsy, requiring a significant suspension of disbelief. After an awkward encounter at Valerie's apartment, Adam and Miranda agree to daily walks, during which Adam will show Miranda his favorite corners of the city. As they admire churches, fountains and Bernini sculpture, they converse, cautiously at first, angrily at times, and then with increasing sympathy and ardor.

The two met as teenagers and were each other's first loves, destined — so they and their families thought — to marry. But then Adam committed a betrayal that shattered the relationship and flung their lives in different directions. He is eager now to reassure himself that "the harm I did was not so great." Gordon reveals the story behind their split gradually, in the novelistic equivalent of the Dance of the Seven Veils.

One of Gordon's most obvious concerns is the shifting nature of identity. "Only he can give her a particular kind of information that at her age seems crucial," Gordon writes, channeling Miranda. "Is she the person that she was?" Yet Miranda already knows that she has changed. Now that they are both parents, she decides a few pages later, "we are not who we were."

Later, she will tell Adam: "I might no longer be that person you knew. Or thought you knew." He asks, reasonably enough: "Who are you then?"

Such exchanges quickly grow tedious. The novel is far more entrancing when Gordon abandons her conceit of the Roman holiday and flashes back to the original romance. Miranda and Adam were drawn together by the passion and innocence of youth and Miranda became happily entangled with Adam's family. But the lovers responded differently to the tumult of the 1960s. Adam doubled down on his musical gifts, isolating himself, while Miranda opted for political engagement. Even if Adam hadn't broken Miranda's heart, a marriage between them might well have been a disaster.

Back in Rome, even Miranda seems to be having her fill of reflection and badinage. "She's tired of it all," Gordon writes, "the crowded noisy city where she does not understand and is not understood, the endless talk with Adam, full as it is of unanswerable questions. Am I the person who I was? What has become of me?"

As the couple move closer and calculate whether to risk renewed intimacy, the novel's slow unfolding begins to pay off. Adam and Miranda touch. She understands, for the first time, the extent of his suffering. They ponder all they have to lose. And as "the endless talk" subsides into silence, Gordon deftly awakens the strains of regret and desire that we too feel as we watch old loves and old selves recede.

Klein is a cultural reporter and critic in Philadelphia and a contributing editor at Columbia Journalism Review. books@latimes.com